1. Technical Field of the Invention
The present invention relates to a battery pack containing rechargeable batteries, an electrical device connectable to this battery pack, and a method of identifying the type of a battery pack.
2. Description of the Related Art
Battery pack contains rechargeable batteries (secondary batteries), which can be repeatedly recharged, such as nickel-cadmium batteries, nickel-hydrogen batteries, and lithium-ion batteries. Since there are many different types of electrical devices which use battery packs, such as portable electrical equipment, there are also many different types of rechargeable batteries housed in battery packs. In particular, the rated voltage of a rechargeable battery is specified according to the electrical equipment to which the rechargeable battery is connected, and it is necessary to connect a battery pack containing rechargeable batteries suitable for the type of electrical equipment. Consequently, a battery pack provided with a signal terminal, which allows the electrical equipment to identify the type of battery pack connected, has been developed.
Battery pack is designed to properly provide power to electrical equipment connected to the battery pack under specified conditions. Some battery packs have protection circuits such as over-charge, or over-discharge prevention circuits to protect the battery packs and the main units of electrical equipment. However, in some cases, compatible battery packs such as so-called pirated articles do not have such protection circuits. In these cases, occurrence of voltage variation may cause not only improper operation of electrical equipment units but also damage of the electrical equipment units or the battery packs themselves. Accordingly, in order to protect an electrical equipment unit by detecting use of such a false battery pack, it is necessary to identify whether a battery is authorized.
There are a battery pack and an electrical equipment unit using this battery pack both of which have signal terminals for communication additionally to positive and negative electrode terminals for charging/discharging. The signal terminals are used for identification of an authorized battery. FIG. 1 shows an example of a battery pack and an electrical equipment unit serving to perform the identification of an authorized battery. With the electrical equipment unit 501 and battery pack 502 shown in this figure, certain information is transmitted from the electrical equipment unit 501 to the battery pack 502 through signal terminals. Then, the battery pack 502 inputs the information received from the signal terminal in a predetermined function, and returns the result to the electrical equipment unit 501. Subsequently, an electrical equipment unit 501 compares the transmitted information and the returned result, and detects whether the result is obtained by the predetermined function or not by means of an electrical equipment control portion 515. When the result of detection is correct, the battery pack 502 is identified as an authorized battery, when the result is not correct or is not returned the battery pack 502 is identified as a false battery, and a display portion 516 displays the result of the identification.
However, there is a problem that the above identification method cannot sufficiently eliminate false battery packs. The reason is that false battery packs can have signal terminals and the function can be set in the signal terminals. For example, if a manufacturer of a false battery pack monitors communication data in the signal terminal by using an authorized battery pack and can guess the relation between an input value and an output value, the manufacturer can install a mechanism calculating similarly in the false battery pack. Accordingly, such a method identification of which can be guessed based on an input value and an output value cannot eliminate false battery packs which have mechanisms calculating similarly to the authorized battery pack. There is a problem that false battery packs with low quality cannot be surely eliminated.
Patent Document 1: Japanese Patent No. 3341302
Patent Document 2: Japanese Laid-Open Patent Publication TOKUKAI No. 2000-200222
Patent Document 3: Japanese Laid-Open Patent Publication TOKUHYO No. HEI 9-500520